The invention relates to a method for separating partial webs in a slitter winder. In particular the invention relates to a method for separating partial webs in a slitter-winder, in which method the partial webs are separated by spreading in a spreading device having at least a first, bowed spreader roll fitted at one side of the partial webs and a second, bowed spreader roll fitted at the opposite side of the partial webs.
It is known that a fiber web, e.g. paper, is manufactured in machines which together constitute a paper-manufacturing line which can be hundreds of meters long. Modern paper machines can produce over 450,000 tons of paper per year. The speed of the paper machine can exceed 2,000 m/min and the width of the paper web can be more than 11 meters.
In paper-manufacturing lines, the manufacture of paper takes place as a continuous process. A paper web completing in the paper machine is reeled by a reel-up around a reeling shaft i.e. a reel spool into a parent roll the diameter of which can be more than 5 meters and the weight more than 160 tons. The purpose of reeling is to modify the paper web manufactured as planar to a more easily processable form. On the reel-up located in the main machine line, the continuous process of the paper machine breaks for the first time and shifts into periodic operation.
The web of the parent roll produced in paper manufacture is full-width and even more than 100 km long so it must be slit into partial webs with suitable width and length for the customers of the paper mill and wound around cores into so-called customer rolls before delivering them from the paper mill. This slitting and winding up of the web takes place as known in an appropriate separate machine i.e. a slitter-winder.
On the slitter-winder, the parent roll is unwound, the wide web is slit in longitudinal direction on the slitting section into several narrower partial webs which are wound up on the winding section around winding cores, such as spools, into customer rolls. When the customer rolls are completed, the slitter-winder is stopped and the wound rolls i.e. the so-called set is removed from the machine. Then, the process is continued with the winding of a new set. These steps are repeated periodically until paper runs out of the parent roll, whereby a parent roll change is performed and the operation starts again as the unwinding of a new parent roll.
Slitter-winders employ winding devices of different types, for example multistation winders and carrier roll winders, also called two drum winders. In the carrier roll winders the partial webs are wound around winding cores supported by two carrier rolls to partial web rolls via a nip between the carrier rolls and the partial fiber web roll being formed. In the carrier roll winders also a belt arrangement i.e. a so-called set of belt rolls located around two guide rolls can be used as the carrier roll. On slitter-winders of the multistation winder type, the web is guided from the unwinding via guide rolls to the slitting section where the web is slit into partial webs which are further guided to the winding roll/rolls on the winding stations into customer rolls to be wound up onto cores. Adjacent partial webs are wound up on different sides of the winding roll or on different winding rolls. Multistation winders have one to three winding rolls and in them each partial web is wound to a partial web roll in winding stations. During winding a winding nip is formed between the winding roll and the partial web roll to be wound.
In the following description and claims, the term carrier roll is used for simplicity when referring to a support roll or set of rolls of a windup of carrier roll type i.e. including both a carrier roll and a set of belt rolls. Additionally in this description, the term core means also other types of winding tubes used and suitable for use in windups of carrier roll type. Furthermore in this description, partial webs being wound on the winder and partial web rolls being formed are referred to, according to context, either in singular or plural referring to partial webs and web rolls handled in the winder.
In the slitter-winders after the slitting of the fiber web into the partial fiber webs the partial fiber webs are guided via a separating device to the winding device, which separating device separates apart the partial fiber webs in lateral direction in order to avoid the overlap of partial webs and to set the path of partial webs to correct position for winding and in carrier roll winders, so that the partial web rolls to be wound do not adhere to each other at their ends. Typically the length of each winding core corresponds to the width of the partial web to be wound. The separation of the partial fiber webs is usually performed by means of spreading of the partial webs in the lateral direction such that the partial webs will be after the spreading a distance apart from each other. In the spreading of the partial webs, the objective is to perform the lateral shifting of the partial web such that lateral gliding of the partial web on the spreader member is avoided. This is accomplished by guiding the web by means of a first spreader member which deflects the partial webs outwardly toward the sides of the first spreader member, and by means of a second spreader member which restores the partial webs to the original direction. In prior art as spreader members for example rods, beams, rolls or revolving roll mantles mounted on an axis bent into curved form are employed. A revolving roll mantle may be composed of rigid mantle units or continuous and elastic mantle units. The mantle units may also be separate.
As described above there are many types of spreading system in common use. Some have a single element, while others have two or more elements. A dual bowed roller spreader uses two conventional fixed bow spreaders to produce some very powerful spreading effects and its primary use is after slitting. The dual spreader arrangement allows a folding type of web separation and the dual spreader assembly maintains an equal path length from unwind to windup and thus does not affect the web tension profile. The dual spreader is the most powerful device to separate the cut webs and to create desired narrow gaps between the wound rolls.
As is well known from the prior art the extent of the separation distance between the partial webs is adjusted by altering the curve radius or by altering the distance between the spreader members or by altering the wrap angle of the partial web. If the adjustment is made by altering the curve radius of the spreader member used in spreading the partial webs, high precision is needed, since even a little change in the curve radius has a strong effect on the distance between the partial webs. The most common way of adjusting the separation distance between the partial webs is to adjust the angle of wrap of the web across the spreader members or the rolls. Thus the web makes a steeper or less steep angle when it passes over the spreader members or the rolls, whereby the separation distance between the partial webs is changed. When the angles of wrap of the web at the spreader members or rolls are changed, the directional angles of the arcs relative to the web are also altered. An error in the directional angle of the arc causes a lateral component of rolling in the partial web, which causes problems, because this creates friction force, which tend to move the partial web sideways off from the paths of the partial webs, when rotating rolls are used as spreader members.
The prior art discloses different arrangements and methods for separating partial webs by spreading devices. For example in EP patent publication 0431275 is disclosed a device for spreading of partial webs comprising a first, bowed, revolving roll fitted at one side of the web and a second, bowed, revolving roll fitted at the opposite side of the web, as well as a swing mechanism, which is fitted to act upon said rolls so as to alter the wrap, i.e. deflection angles, of the component webs and thereby to produce the desired spreading of the component webs. The device is provided with a regulation mechanism, which is fitted to correct the directional angles between said rolls and the web to the desired values with all values of the deflection angle.
In U.S. Pat. No. 3,765,616 is disclosed an apparatus to laterally space a plurality of strips which have been slit from a relatively wide web to enable individual rewinding of the strips. The apparatus comprises lead-in and lead-out rollers with a pair of guides disposed between said rollers, said guides being arcuate transversely of the plurality of strips. The arcuate guides serve to twist the strips from a coplanar relationship and to deviate their paths from each other and then twist them back into coplanar but spaced relationship. The guides are angularly adjustable to arrange the arcs in predetermined relationship with respect to each other and to the lead-in and lead-out rollers respectively and also are supported by pivotably mounted arms or frames to adjust the degree of arc to which the strips are subject.
In CA patent publication 2,066,450 is disclosed an apparatus for spreading (broad-drawing) of webs with two curved spreading elements that are rolled shaped in the wrap-around area and coupled to each other and supported pivotably in a frame. The spreading elements are each secured to the coupling element of a four-bar linkage, the two driving levers of the two four-bar linkage being coupled with each other through a gearing system so as to be pivotable in the same direction.
In U.S. Pat. No. 3,463,377 is disclosed a mechanism for separating strips of a traveling web comprising first and second supporting means having support areas positioned to form an arc. The mechanism comprises also first arc changing means connected to the first supporting means for changing the curvature of the arc thereof and second arc changing means connected to the second supporting means for changing the arc thereof, whereby the separating effect of said supporting means can be adjustably controlled.
In F1 patent publication 121306 is disclosed a device for separating partial webs comprising at least a first, bowed roll fitted at one side of the web and a second, bowed roll fitted at the opposite side of the web, as well as a mechanism, which is fitted to act upon said rolls so as to alter the wrap angles of the component webs and thereby to produce the desired spreading of the component webs. The device is provided with a regulation mechanism, which is fitted to change the distance between the first and the second roll dependent of the effecting deflection angle of the partial webs and thus creating the desired separation of the partial webs. The mechanism is a swing mechanism and it is adapted to increase the distance between the first and second rolls simultaneously when the deflection angles of the partial webs is increased.
In prior art methods using a deflection spreading method for separation of partial webs the deflection spreaders for partial web separation the arcs of the spreader rolls are of fixed form, for example of circular arc form, also the direction of the arcs relative to the web is parallel and the arcs of each of the spreader rolls are substantially the same as well as the deflection over each of the arcs of the spreader rolls is equal and the structure of the adjustment mechanism is such that the web entering the deflection spreading device and the web leaving the deflection spreading device are substantially parallel at all wrap angles.
The prior art deflection spreading devices are functional as such but in some cases due to the layout of the slitter-winder and the path geometry of the web the above types of deflection spreading devices are not applicable in all slitter-winders. In particular problems are caused by the parallel entering and leaving direction of the partial webs to and from the deflection spreading device and position of spreader rolls and adjustment devices influencing the entering and leaving direction, which in practice require a lot of space and thus limit the path geometry of the webs.